So, after a discussion with an expert from my trade union, I decided to accept the "offer" and quit. The next day, I made sure I had documened every loose end and copied all relevant data on my workstation to the servers, I wrote a good-bye mail, cleaned my desk, zeroed the disk of my workstation ("F*CK YOU!" written in 1011 zeros ...), stuffed all of my private equipment into my car and left.
I didn't bother the trade union. I'm not able to litigate; had I done so, I would have lost, not for the cause, but for some meaningless detail (which happened to me before). So I accepted the offer, which was indeed what you described. But I had no chance to document and copy over. Immediately after they had knowledge that I read their firing letter (I dialed them up to ask what this was all about), they closed down my account and my VPN access. So, they didn't even get the last pending commits.
The youngsters will surely port all my perl stuff to or replace it with python. But they don't have time! They are churning out classes after classes elsefor, I know that. And that won't change in the near future. So, they might want to come to my toilet to drink water. I might be available, who knows.